Microstrip antenna design candidates for 20/30 GHz personal communications

Because of low profile planar configuration, light weight, and ease of fabrication microstrip antennas are attractive candidates for personal communication applications. In array forms, they can be used to provide high gains to replace conventional antennas, such as the paraboloid and dual reflector antennas. However, at high EHF frequencies the resistive losses associated with their feed network and the dielectric substrate reduce the array available gain and degrade their achievable G/T. These problems are partially overcome in some designs, such as those using the low loss non-radiating dielectric lines, but their performance is so far inferior in gain and sidelobe levels. Alternative planar antennas using suspended and triplate lines have also been developed that perform well at lower frequencies, but at EHF frequencies are still too lossy. A possible means for overcoming the loss problem in microstrip antenna arrays at EHF frequencies is to distribute the active devices in the array, thereby eliminating problems associated with their feed network loss. However, conventional microstrip arrays have large number of elements, and incorporating large number of active devices in the array increases the array cost, not desirable for low cost applications. In practice, the cost of active devices can be reduced by monolithic fabrication technology, such as MMICs. In addition, one may use subarrays of microstrip patches to reduce the required number of MMIC modules. However, the size and gain of subarrays affect the array gain. The latter can be controlled by eliminating the subarray size, but an investigation is necessary to determine its affect on the array gain and sidelobes. It remains to reduce the subarray losses, which may be accomplished by the design of new radiators. This paper presents the result of study for subarraying effects on the array performance, to determine the usefulness of the concept for EHF applications. The design of low loss subarrays, or radiators, is left for a further study